Neutral ground bonding relay????

Discussion in 'OnBoard Electronics & Controls' started by cgoodwin, Feb 20, 2015.

  1. cgoodwin
    Joined: Mar 2011
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    cgoodwin Junior Member

    OK here is what I have:

    Xantrex SW4024 inverter/charger
    Silent partner 6.5kw genset
    30amp Shore power

    I am trying to find a relay which will automatically transfer from shore to inverter in the event of shore power loss and that will switch from inverter or shore to genset if the genset is started. I would also like something which deals with breaking the neutral ground bond when appropriate...

    Does anyone know of such an animal exists?
     
  2. Ike
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    Ike Senior Member

  3. cgoodwin
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    cgoodwin Junior Member

    It does not make and break the ground neutral bond...
     
  4. AndySGray
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    AndySGray Senior Member

    You could probably set something up using a couple of Contactors - like a relay but much higher current rating - very common for three phase so you could use one channel to make or break the neutral/ground connection.

    Energise coil from shore feed on one and from the genny on the other ?
     
  5. groper
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    groper Senior Member

    Yes, no need to buy expensive "products" which do what you need... Simply use contactors that have normally open and normally closed contacts. They are commonly found in the 4 pole variety at any electrical wholesaler, 3 poles are typically normally open, and 1 pole is normally closed. AC coil for control. There are other combinations of poles and many different types, but the one I mention above is very common and easy to find just about anywhere.

    For the shore power, you simply run an active and neutral control wire from the shore supply side to the contactor control coil, typically a1 and a2. This will actuate the contactor whenever there is shore power available and close 1 pole which makes your shore power connection to your distribution switchboard for all your house loads. At the same time, you run the inverter supply through your normally closed pole, which will automatically break the inverter connection as the contactor actuates. So you get an almost instant changeover, the slight delay is only the time it takes the contactor to physically close. It is slow enough however, to prevent both supplies shorting in the process of change over.

    You simply do the same thing with your generator, or what I'd prefer to see is it fed from a double pole generator changeover switch. If you have to manually start the generator, then you might aswell throw a switch whilst your there, it doesn't really need to be automatic. Although you could make it automatic, by simply using another contactor, and using the same mechanical lockout function to ensure that the generator cannot be connected to either shore power or inverter supplies.

    Edit, if you want make or break your earth neautral bond, (when on shore power you should not have a main earth neutral connection as there is already an MEN in the marina distribution board) you simply have to run it through another pole of a contactor, remember you can daisy chain an unlimited number of contactors, so that when shore power is active the pole is open and as soon as shore power is disconnected, it will automatically close- so you should use a normally closed pole for this which is held open by the shore supply when it's available.
     
  6. cgoodwin
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    cgoodwin Junior Member

    Yes, I understand that there are an infinite number of relay possibilities, the switching is simple and there are a myriad of transfer switches available. The question I am asking relates tot he switching of the neutral ground, this is complicated. The neutral and ground are bonded inside the generator, code also requires only one ground on the vessel and that it is to be shared with the DC negative, by having more than one bonding point the ground circuit could become hot when on gen power AND the stray current in the AC system could turn the hull into a battery causing severe corrosion.... What I am seeking is a diagram.
     
  7. AndySGray
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    AndySGray Senior Member

    Don't over think it

    Wire it like there is no bonding keeping G and N separate

    A generator contactor with three poles would simultaneously break the Hot, Neutral and Ground from the generator (effectively isolating the generators G N bonding from the circuit when it is not being used)
    - so with the genny off there is no current to energise the coil and all three poles are open.

    It is almost like the gen doesn't exist.

    There are as Groper said 'paired' contactors with a mechanical interlock so that if one if closed the other is locked out preventing you from having both the shore power and generator energised at the same time.

    I beleive the Furrion units in the link Ike provided do have that feature though yes, their wiring diagram sucks.
     
  8. philSweet
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    philSweet Senior Member

    It may work best to have two relays. One to switch between shore and inverter (auto or manual). The second one disconnects shore/inverter and connects genset (with a warm up time delay). Your generator maker sells a transfer switch accessory, so I would probably use that one.

    So if you do it that way, can you now draw a circuit and show where and when the neutral needs to be broken? Please show the bonding system also. There have been several threads similar to this in the past, but there always seems to be a quirk or some regulatory conflict in play regarding the hull bonding system.
     
  9. groper
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    groper Senior Member

    The neutral ground bond, is called an MEN connection here in Australia, we say earth instead of ground etc. Every house has one in the switchboard as part of the multiple earth neutral system. Inside the house, this is never to be repeated or there is risk of circulating current. Same applies in your boat. When on shore power, you already have an earth neutral bond on the supply side of the marina distribution board, therefore you should not have another inside your boat when on shore power.

    Most small inverters, are treated as isolation transformers, and they do not need an earth. Because they are not earthed, a person cannot receive an electric shock via an earthed situation - there is no path for current to flow through a person to earth. So the only way you can receive a shock is to come between neautral and active, ie you become a load. An RCD (Australian term for safety switch, or residual current detector, earth leakage detector etc) cannot protect you in this situation either, so if this happens its a dangerous situation no matter what type of electrical protection you care to employ.

    When your on generator power, there is no MEN from the marina supply, therefore you can have one inside the generator. Just as the neutral and earth bond exists at a power station and every transformer forming a multiple earth distribution network. It provides a path of very low resistance, back to the supply and enables circuit breakers and RCDs to operate. So when you change over to generator power, you need to switch all 3 poles, active neutral and earth. You already have your Neutral earth connection inside the generator, so you don't need to ( and should not) provide another MEN connection.

    Same applies to shore power, switch all 3 poles over the shore, the earth neutral bond then is intact inside the marina switchboard, and you still don't need ( and shouldn't ) provide another anywhere on your boat.

    It's upto you, whether or not you provide a DC negative and AC earth bond, do what ever rules dictate in your area. You can simply make or break this bond through another contactor if that's what you need to do. I don't see how AC currents can cause corrosion however, it's more about using a single bonding point on the through hull to do 2 jobs... Galvanic protection on the DC and earthing for the AC...
     
  10. cgoodwin
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    cgoodwin Junior Member

    Interesting. I have a reversing relay made by Struthers-Dunn that handles the switching for my winch, it has 3 spdt contact sets and two coils. With neither coil energized all contacts are broken, it is mechanically impossible to close both sides of the contacts at the same time. So in one position all three center poles are connected to the contacts on the left, and in the other they are connected to the contacts on the right. They have a 30 amp version here: http://relays.struthers-dunn.com/Asset/575_Series.pdf
     
  11. cgoodwin
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    cgoodwin Junior Member

    Still having issues laying it out...
     
  12. AndySGray
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    AndySGray Senior Member

    OK from your diagram / pdf,


    Shore
    ---------
    1, 4, 7 are the Hot, Neutral and Ground respectively FROM marina.

    1 and 4 would also be connected to energise the left hand coil.

    I would probably wire a GCFI breaker in there too,

    Good idea to wire a bulb / buzzer between 4 and 7 - this is your reverse polarity warning if some muppet got the wiring @rse about face at the Marina.



    Genny
    ---------
    3, 6, 9 are the equivalent Hot, Neutral and Ground respectively FROM the generator.

    9 may not have a wire from the gen so OK bridge 6 & 9 if there are only 2 wires (Hot and Neutral) from it.

    3 & 6 Energise the RH coil



    Output
    ----------
    2, 5 and 8 are OUT to your Distro panel.


    Inverter
    -----------
    The Xantrex can connect
    AC1 IN to 1
    AC2 IN to 3
    Neutral1 to 4
    Neutral2 to 6

    Neutral OUT to 5
    AC OUT to 2

    Chassis to 8



    The relay will be OK for a marine environment if you're already using one, and it simplifies the spares situation as you can carry a spare which will work for both winch and panel.

    Would highly recommend you get someone to check your work (and my logic :p) before using it in earnest
     
  13. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    My Onan marine gen has the neutral-ground bond permanently wired at the gen set. Good because hots will short to ground in appliances keeping you from shock.

    My 4PDT relay that switches shore and gen breaks the neutral connection to boat power when on shore power, so gen's neutral- ground bond does nothing, the neutral for gen is open circuit.

    [​IMG]
    http://www.zoro.com/i/G4302934/?utm...KsRiZszNR9ZmysYjIoF6UVrVDpwUxfX9cUhoCserw_wcB

    Ebay a good cheaper source for these.

    two of these connected together can switch between 3 sources of power for the boat with twin 30 amp power in[puts, which is what I did.
     
  14. cgoodwin
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    cgoodwin Junior Member

    Nice, do you have a diagram?
     

  15. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Not nice (how many amps is your genset?). Buy the one from Westerbeke - the one that they designed to work with your genset. It will come with a diagram. I'm betting your inverter/charger also came with a diagram.
     
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